Improved quantification of catechin and epicatechin in red rice (Oryza sativa L.) using stable isotope dilution liquid chromatography-mass spectrometry

Abstract

Epimerization can change the catechin content and composition of samples during extraction and analytical analyses. To control the effect of epimerization, we developed a novel and stable isotope dilution liquid chromatography-mass spectrometry (LC–MS) method using catechin-2,3,4-13C3 and epicatechin-2,3,4-13C3 as stable-isotope-labeled internal standards (SIL-ISs). When the SIL-ISs were used, the catechin and epicatechin contents were stable (104–109% and 100–109% of the initial concentration, respectively) despite long storage times. In contrast, when L-2-chlorophenylalanine was used as an internal standard, catechin and epicatechin concentrations of 88–97% and 164–277% of the initial concentration, respectively, were obtained after long storage times. Furthermore, the least significant epimerization effect and highest extractability were observed when extraction was performed at 70 ℃ for 30 min. The recoveries for red rice using the developed isotope dilution LC–MS method at two different concentrations were between 100.72 and 118.67%, with relative standard deviations less than 3.67%.